1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus, an image pickup system, and a driving method of the photoelectric conversion apparatus.
2. Description of the Related Art
As a photoelectric conversion apparatus configured to output signals that can be used for focus detection by a phase difference detection method, a photoelectric conversion apparatus having pixels, each including a microlens and a pair of photoelectric conversion elements corresponding thereto, has been proposed.
In such a photoelectric conversion apparatus described in Japanese Patent Laid-Open No. 2013-211833, a region for acquiring both focus detection information and image information and a region for acquiring only image information are defined. From each pixel in the region for acquiring both focus detection information and image information, a signal (signal A) based on only one of photoelectric conversion elements in a pair and a signal (signal A+B) based on charges generated in both the photoelectric conversion elements, are read out. From each pixel in the region for acquiring only image information, only the signal A+B is read out (i.e., the signal A is not read out) to shorten the readout time.
In the two signals A+B described in Japanese Patent Laid-Open No. 2013-211833, there may be variation between signals for an image (image signals) due to a difference in transfer characteristics or the amount of produced noise, caused by a difference in readout method.